Margaret Chan Fung Fu-chun is all too aware that the world can't be changed overnight. 'Working in public health means constantly working for co-ordination and collaboration across all sectors of society with a broad range of stakeholders,' says Chan, director-general of the World Health Organisation (WHO) and the first Chinese to run a United Nations agency.

For nearly five years, Chan has been at the forefront of global efforts to tackle health threats, leading WHO in its support for countries battling diseases from HIV/Aids to cancer. Her job requires exceptional leadership skills, a talent for negotiation and a commitment to making a difference. It also calls for resilience, for the process of co-ordinating responses and settling disputes is invariably protracted.

Former director of health in Hong Kong, Chan joined WHO in 2003 as director for protection of the human environment. She became director-general in 2006 after the unexpected death of her predecessor, Lee Jong-wook.

Chan says she gained invaluable knowledge from fighting avian flu and the severe acute respiratory syndrome epidemic in Hong Kong. 'A new disease is, by nature, poorly understood. Decisions with far-reaching consequences must be made quickly,' she says, adding that health officials must convey a sense of control while admitting the unknowns. Seeking help from outside experts is important, she says, and so is meeting the public.

Chan, who is seeking re-election next year, is proud of WHO's work in preparing for influenza pandemics, especially in terms of vaccine availability, antiviral medicines and diagnostic tests in the developing world.

'That the H1N1 [swine flu] influenza virus responsible for the 2009 pandemic was so mild was certainly the luckiest event during my administration,' she says. 'I was proud of the way the world responded and of how lessons learned have been taken forward.'

Chan also cites last December's launch of a vaccine to prevent meningitis epidemics in Africa as a key achievement. 'In this case, the best technology the world could collectively offer was introduced in Africa,' she says. 'The vaccine represented a new age of international collaboration with the goal of bettering health.'